The engineering of developmental regulation

It is fast becoming clear that, to understand the complexity of biological systems, it is not enough just to have mechanistic explanations for how things happen. We also need explanations for why things are there, i.e. what it is about particular states of affairs that enabled them to have been selected for. Among Systems Biologists, it is often asserted that “strategic” goals—things like robustness, speed, noise‐filtering, flexibility, adaptability, etc.—are likely to be the major drivers of complexity, more so than, say, physical constraints or “frozen accidents” of evolution. Animal development provides a wonderful context in which to explore this idea, because a wealth of experimental research has revealed the existence of bewilderingly complex, yet extremely highly conserved, networks of gene‐ and cell‐cell regulation. I will focus on two broad areas—morphogen‐mediated pattern formation and intrinsic tissue growth control—in which exploratory modeling, together with targeted experimentation, gives plausible glimpses of underlying “design principles”. I will discuss concrete examples in which the need to meet multiple performance objectives seems to justify complicated regulatory architectures.